Malate Uptake into Isolated Vacuoles from Catharanthus roseus Cells: Role of the Membrane Potential

The mechanisms involved in the transport of malate into isolated vacuoles of Catharanthus roseus (L.) cells were investigated with special reference to the effects of induced changes in membrane potential and surface charges of the tonoplast. For this purpose, thiocyanate (SCN^?), a highly permeant anion often used as a membrane potential probe, was extensively exploited. In the absence of Mg-ATP, the low accumulation ratio of ¹⁴C SCN^? could be related to the presence of negative charges at the outer surface of the tonoplast exerting a screening effect on the displacement of lipophilic anionic species. Nevertheless, malate was taken up continuously by vacuoles supporting the concept of a transport component which facilitates its transfer through the tonoplast. From experiments showing the pH dependence of malata uptake, it is suggested that the protonated form of the transporter is implicated in this process. Moreover, when the vacuoles are energized by Mg-ATP, the study of the equilibrium distribution of ¹⁴C SCN^? indicated an inside positive membrane potential difference. Advantage was taken of these results to modulate the membrane potential with high levels of thiocyanate. The data obtained demonstrate that malate uptake results from electrophoretic movement in response to the positive potential difference.     

Gene induction during differentiation of human monocytes into dendritic cells: an integrated study at the RNA and protein levels

Changes in gene expression occurring during differentiation of human monocytes into dendritic cells were studied at the RNA and protein levels. These studies showed the induction of several gene classes corresponding to various biological functions. These functions encompass antigen processing and presentation, cytoskeleton, cell signalling and signal transduction, but also an increase in mitochondrial function and in the protein synthesis machinery, including some, but not all, chaperones. These changes put in perspective the events occurring during this differentiation process. On a more technical point, it appears that the studies carried out at the RNA and protein levels are highly complementary.     

HD-187, a new isolate of Bacillus thuringiensis that produces high yields of δ-endotoxin

HD-187, a new isolate of Bacillus thuringiensis serotype 5 (5a,5b), produced higher yields of δ-endotoxin than any other isolate previously tested at the laboratories of the Agricultural Research Service of the U.S. Department of Agriculture at Brownsville, Texas. Recoveries of as high as 2,000 × 10⁶ international units (2,000 mIU)/liter of harvested beer were achieved from fermentations of HD-187, giving products with potencies as high as 200 × 10³ (200 kIU)/mg. These contrasted with recoveries of about 200 mIU/liter and products with potencies of about 15 kIU/mg obtained in fermentations of HD-1, the strain of B. thuringiensis serotype 3 (3a,3b), that is used in most commercial production of the δ-endotoxin.     

Biosynthesis of sulfated proteoglycans in amphibian embryonal cells

The synthesis of sulfated proteoglycans in small explants from various parts of late blastulae fromAmbystoma mexicanum orXenopus laevis was investigated by incorporation of radioactive sulfate or glucosamine and galactosamine in media of low, normal or high tonicity. The explants differentiated into ciliated aggregates or fibroblast-like cells, or remained undifferentiated depending upon their origin in the embryo. High tonicity induces the explants to dissociated and prevents morphological differentiation, while low tonicity hardly affects this process. Yet, both types of media decrease the incorporation into glycosaminoglycans to various degrees, ranging from 40 to 80%, depending upon the species. InXenopus, the uptake of sulfate is inhibited by as much as 90% in high tonicity media. The rate of incorporation of label is approximately twice as much in mesodermal as in animal or vegetal aggregates, which do not differ significantly. Animal aggregates fromAmbystoma, however, revealed an exceptionally high uptake of sulfate. The relative distribution of chondroitin sulfates and heparan sulfates is not affected by changes in tonicity, except inXenopus where high tonicity severely suppresses the synthesis of heparan sulfates, and is independent of the type of aggregate. The relationship between the synthesis of sulfated proteoglycans and processes involved in cell differentiation, especially cell adhesion, is discussed.